Window glass antenna for a motor vehicle

ABSTRACT

A pair of antenna conductors are formed on upper and lower blank portions outside an area where defogging heater wires are attached on a window glass of a motor vehicle. One of the antenna conductors is RF-coupled with the defogging heater wires and a feed terminal thereof is located at a lateral side of the glass. The other antenna conductor has a feed terminal located at another lateral side of the glass. A pair of reception signals complement with each other in directivity due to asymmetric characteristic of the antenna conductors and are used in a diversity reception system for obtaining a nondirectional reception characteristic.

This is a continuation of application Ser. No. 07/557,957, filed Jul.25, 1990, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a glass window antenna for a motorvehicle, wherein antenna conductors are arranged on a surface of awindow glass used as an insulator.

2. Description of the Prior Art

In an antenna system of a motor vehicle, a diversity reception using aplurality of antennas is employed for reducing changes in reception gainaccording to traveling direction of the vehicle. An FM broadcastdiversity reception, for example, a pole antenna attached on the body ofthe motor vehicle and an antenna comprising an antenna conductorattached on a rear glass window are used in a prior art. A spacediversity reception is so performed that the highest level one inreception signals is selected (cf. Japanese laid open patent applicationNo. 140301/1985).

It is known to perform diversity reception with two or more antennaconductors and feed terminals on a rear window surface of the motorvehicle (Japanese utility model registration application laid open Nos.138408/1988 and 29307/1988 and a patent application laid open No.269625/1988).

As to the pole antenna, tuning adjustment is possible only with regardto its length. It is less flexible in arrangements of conductor thanthat of a glass window antenna. It is therefore difficult to tune theconductor for providing complementary directivity for diversityreception system. An element of the pole antenna is arranged verticallyso that it shows a low reception sensibility to receive horizontallypolarized wave.

It is possible to tune directivity of respective antennas in diversityreception system in which spaced conductors arranged on a surface of aglass window. Spaces on the window, however, are little for the antennaconductors so that they show low average reception sensibility.Preamplifiers with fixed gains must be inserted immediately after feedterminals of the antenna conductors. These fixed gain amplifiers oftensaturate at strong radio wave field so that reception radio voice isremarkably degraded.

OBJECT AND SUMMARY OF THE INVENTION

Accordingly it is an object of this invention to provide window glassantennas which have good complimentary directivities and high receptionsensibilities without using preamplifiers.

In accordance with an aspect of the present invention, there is provideda window glass antenna of a motor vehicle comprising heater wires formedin a heating area on a window glass of the motor vehicle; a firstantenna conductor formed in a lower blank area outside the heating area;a second antenna conductor formed in a lower blank area outside theheating area and RF-coupled to the heater wires; and first and secondfeed terminals arranged oppositely at both lateral sides of the windowglass for deriving reception signals from the first and second antennaconductors.

According to opposite wiring courses toward the feed terminals, locationof the first and second antenna conductors is asymmetrical with respectto a center line of glass window. Directivities of the antennaconductors complement with each other. Non-directional receptioncharacteristic is thus achieved by diversity reception.

The above, and other, objects, features and advantages of the presentinvention, will become readily apparent from the following detaileddescription thereof which is to be read in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a rear glass window on which a glass windowantenna for a motor vehicle according to this invention is provided;

FIG. 2 is a graph showing directivities of upper and lower antennaconductors;

FIG. 3 is a graph showing variation of reception sensibility withrespect to coupling capacity between heater wires and the second antennaconductor;

FIG. 4 is a graph showing a gain of the first antenna conductor forvarious line width of feeder line connected thereto;

FIG. 5 is a graph showing gain of the second antenna conductor in a casein which a horizontal element is added to a bus bar of heater wires anda case in which the horizontal element is not provided;

FIG. 6 is a graph showing gain of antenna in a case in whichshort-circuit conductor and horizontal elements are added and anothercase in which these are not provided; and

FIG. 7 is a graph showing gain of antenna in a case in which horizontalelement is provided to capacitively couple to the first antennaconductor and another case in which the horizontal element is notprovided.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 is shows a rear glass window of a motor vehicle according to thisinvention. In the middle zone of the glass window, a plurality ofdefogging heater wires 2 is formed in parallel to each other through aprinting and a baking processes. The heater wires 2 are divided intoupper and lower groups. Power is fed through bus bars 3 and 4 through areturn path via a common bus bar 5. Another power feed system may bearranged in which heater wires 2 are not divided into two groups so thata current flows from a side bus bar to another side bus bar.

The heater wires 2 are used as an AM radio wave reception antenna.Magnetically coupled choke coils 8a and 8b are inserted into powersupply lines 7a and 7b. The choke coils provides the heater wires 2 withlarge impedance to ground in radio frequencies. The power supply line 7ais coupled to a main power supply through a switch 6 and the powersupply line 7b is coupled to ground.

Antenna conductors 10 and 11 are arranged on upper and lower blank areasof the heater wires 2. The upper antenna conductor 10 is exclusivelyused for FM broadcast reception. The lower antenna conductor 11 is usedboth for AM and FM broadcast receptions. A diversity reception isperformed for FM broadcast reception with using the upper and lowerantenna conductors 10 and 11.

Asymmetrical arrangement of conductors is employed with respect to thecenter line of the glass window for satisfactory FM diversity reception.For securing asymmetrical arrangement of the conductors, a feed terminal10a of the upper antenna conductor 10 is located at the right side(viewed from inside of a car) of the glass window 1 and a feed terminal11a of the lower antenna conductor 11 is located at left side.

The antenna conductor 10 comprises horizontal elements 10b-10g. A mainelement 10b is a single element antenna of about 800 mm in length and issymmetrically arranged with respect to the center line of the glasswindow 1. At the center of the conductor 10b, a vertical couplingconductor 10h is connected to form an antenna of generally inverseletter-T configuration. The coupling conductor 10h is connected to afeeder line 10i arranged along an upper edge of the glass window 1. Anend of the feeder conductor 10i is connected to the feed terminal 10alocated at the side end of the glass window 1.

The feeder line 10i is 3 mm in width and made wider than otherconductors so that impedance matching is satisfied between a feedercable of 50Ω to be connected to the feed terminal 10a and the inverseT-antenna comprising the main element 10b and the coupling conductor10h. The feeder line 10i has a desired capacitance to ground which isproduced by capacitive coupling to a window frame (ground potential)near the upper edge of the glass window. A desired impedance measured atthe feed terminal 10a is obtained.

Horizontal elements 10d and 10f are extended from the bus bar 3 of theheater wires 2 in parallel with the main element 10b. These horizontalelements are capacitively coupled with the main element 10b so as totune the antenna in directivity. Respective ends of the horizontalelements 10d and 10f are located at 300 mm and 400 mm away from thecenter line of the window 1.

A short-circuit conductor 10j of 4 mm in width is provided along thecenter line of the glass window 1 to short all of upper half of theheater wires 2. A horizontal element 10g is extended from an end of thecouple capacitively with the element 10h for improving directivity. Anend of the horizontal element 10g is located at 500 mm away from thecenter line of the glass window 1. The short-circuit conductor 10jconnects equipotential points of the heater wires 2 so that noshort-circuiting current actually flows through the short-circuitconductor 10j.

In this embodiment, line intervals 10d-10b, 10b-10f, 10f-10g and10g-heater wires 2 are respectively 10, 15, 7.5 and 7.5 mm.

A horizontal auxiliary element 10e of 165 mm in length is extended fromthe feed terminal 10a so as to tune the antenna in directivity as wellas high frequency characteristic.

The above-mentioned elements 10d, 10h, 10g and 10e improve receptionelement 10b on the left side thereof. These elements are arrangedgenerally on the right side of the center line of the glass window 1.The antenna conductor 10 is thus arranged asymmetrically in general withrespect to the center line of the glass window 1.

The lower antenna conductor 11 has a horizontal main element 11bextended from the feed terminal 11a in parallel with the heater wires 2at an interval of 2 mm. The main element 10b is capacitively coupled tothe heater wires 2 to serve as an antenna used both in receptions of AMand FM waves induced on the heater wires 2. The lower half of the heaterwires 2 serves as ground circuitry e.g. a return path of a heatercurrent so that noises in a heater power supply do not propagatedirectly from the heater wires 2 to the main element 11b. No remarkablenoises are recognized in a reception signal. An end of the main element11b is located at 210 mm away from the center line of the glass window1.

Auxiliary horizontal elements 11c, 11d and 11e are extended from busbars 3 and 5 of the heater wires 2 for improving directivity andfrequency characteristics of the main element 11b. The heater wires 2are thus tuned as an antenna. The element 11c is extended horizontallyfrom the lower end of the common bus bar 5 by 150 mm away from thecenter line of the glass window with an interval of 30 mm to the heaterwires 2.

The element 11d is extended from the lower end of the bus bar 3 alongthe right side of the glass window 1 and then extended horizontally to aposition 410 mm away from the center line of the glass window 1 with aninterval of 15 mm to the heater wires 2.

The element 11e is extended from the upper end of the common bus bar 5along a corner portion and upper side of the glass window 1 to aposition 150 mm away from the center line.

FIG. 2 shows directivity of antenna conductors 10 and 11 with respect toFM broadcast wave of 95 MHz. The directivity of dotted line D11corresponds to the antenna conductor 10 and the directivity of a solidline D10 corresponds to the antenna conductor 11. As is apparent fromthe directivity chart, a dip in gain of the lower antenna 11 appearingon the right side of a traveling course of a car is complemented by again of the upper antenna conductor 10. In the directivity of theantenna conductor 10, a dip appearing on the left side of a travelingcourse of a car is complemented by a gain of the lower antenna conductor11. A diversity reception is achieved by selecting a higher level one ofreception signals from the complementary antenna conductors 10 and 11 inresponse to comparison of these signals. A stable reception signal isobtained regardless of changes of traveling direction of the car.

The lower antenna conductor 11 functions as an AM reception antenna. Inthis radio band, the heater wires 2 is operable as an antenna conductorsince conductors of the wires are relatively long.

FIG. 3 is a graph showing a relation between AM reception sensibilityand coupling capacitance of the main antenna element 11 to the heaterwires 2. Differences in sensibility are plotted with reference to that(0 dB) of a rear pole antenna of 1200 mm long. The difference reachesthe reference when the coupling capacitance exceeds 60 pF, and saturatesat 70 pF or more. In the embodiment, the main element 11b and the heaterwires 2 are set at an interval of 2 mm to give capacitive coupling notless than 70 pF so that an AM reception signal is obtained by theantenna conductor 11 with a sufficient gain.

FIG. 4 shows reception gains of the upper antenna conductor 10 in FMbroadcast wave ranging 80-90 MHz in cases where width of the feeder line10i in FIG. 1 is 1 mm and 3 mm as respectively shown by a dotted lineand a solid line. As is apparent from the graph, reception gains inlower side and upper side of FM broadcast band are respectively improvedwhen the width of the feeder conductor 10i is set not less than 3 mm.Frequency characteristics are improved over a wide range. The feederline 10i is extended from the center line of the window glass 1 towardright side to the feed terminal 10a and operates as an antenna elementwhich serves to improve reception gain on the right side of travelingcourse.

FIG. 5 shows reception gains of the lower antenna conductor 11 in arange 80-90 MHz in cases where the horizontal elements 11c and 11e areextended from the common bus 5 of the heater wires 2 and these elements11c and 11e are removed, respectively as shown by a solid line A and adotted line B. A condition of FM radio wave current induced on theheater wires 2 is changed by extending the elements 11c and 11e from thecommon bus bar 5 of the heater wires 2, frequency bands each in which agood sensibility is obtained are shifted to each other as shown by thegraph. These elements 11c and 11e are arranged on the left side of theglass window 1 so that it operates to improve reception gain of thelower antenna conductor 11 on the left side of the traveling course.

FIG. 6 shows gain characteristics in a band of 80-110 MHz for a case(solid line A) where the short-circuit conductor 10j is provided to theheater wires in FIG. 1 and the horizontal element 10g is extended froman end of the conductor 10j in parallel to the heater wires 2, andanother case (dotted line B) where these conductors 10j and 10g are notused. State of FM radio frequency current induced on the heater wires 2is changed by attaching these conductors 10j and 10g. Frequency bandhaving good sensibility can be shifted as shown by the graph. Thehorizontal elements 10g is extended on the left side of the glass window1 so that it operates to improve reception gain of the upper antennaconductor 10 on the left side of the traveling course.

FIG. 7 shows reception gains in a band of 80-110 MHz in a case (solidline A) where the horizontal elements 10d and 10f are extended from thebus bar 3 of the heater wires 2 as shown in FIG. 1 to capacitivelycouple with the main element 10b on both sides (upper and lower sides)thereof and another case (dotted line B) where the elements 10d and 10fare not used. Influence to the main element 10b by the heater wires 2can be changed by capacitive coupling of horizontal elements 10d and 10fwith the main element 10b at a distance within 15 mm. Frequency bandhaving good sensibility can be shifted as shown by the graph. Thesehorizontal elements 10d and 10f operate to improve a gain of the upperantenna conductor 10 on the right side of a traveling course.

According to this invention, due to asymmetrical arrangement of thefirst and second antenna conductors with respect to the center of theglass window, directivities complementing to each other are obtained.Good reception characteristics are obtained with diversity receptionregardless of traveling direction of car. Especially, a reception systemin which any preamplifier is not employed can be arranged so that areception signal of high quality is received without distortion even ina strong radio wave field.

According to other features of this invention, reception gains of thefirst and second antenna conductors are improved. Complementarycharacteristics of the firs and second antenna elements are ensured tooperate a diversity reception system with high performance.

What is claimed is:
 1. A window glass antenna of a motor vehiclecomprising:heater wires formed in a heating area on a window glass ofthe motor vehicle; a first antenna conductor comprising a singlehorizontal element and a vertical element forming an inverse T shape inan upper blank area outside of the heating area; a second antennaconductor formed in a lower blank area outside of the heating area andRF-coupled to said heater wires; first and second feed terminalsarranged oppositely at both lateral sides of the window glass forderiving reception signals from said first and second antennaconductors; and means for impedance matching between said first antennaconductor and said first feed terminal including a feeder line of about3 mm is width connecting a central feed point of said first antennaconductor along an upper edge of said window glass with said first saidterminal.
 2. A window glass antenna according to claim 1, wherein a lineconductor coupled capacitively to said first antenna conductor isextended from a bus bar of the heater wires on the side where said firstfeed terminal is arranged.
 3. A window glass antenna according to claim2, wherein said line conductor consists of two elements arranged alongupper and lower sides of the first antenna conductor.
 4. A window glassantenna according to claim 1, further comprising:a short-circuitconductor which shorts the heater wires at the center thereof; and aline element extending toward said first feed terminal from an end ofthe short-circuit conductor in parallel with said first antennaconductor.
 5. A window glass antenna according to claim 4, wherein saidheater are wires are divided into upper and lower groups, saidshort-circuit conductor being provided along the center line of theglass window to short respective centers of said upper group of heaterwires.
 6. A window glass antenna according to claim 1, wherein auxiliaryhorizontal elements are extended from the bus bar of the heater wires onthe side of the second feed terminal in the upper and lower blank areasof the glass window to improve antenna characteristic of the heaterwires.
 7. A window glass antenna according to claim 6, wherein anauxiliary horizontal element is extended from the bus bar of the heaterwires on the side of the first feed terminal in the lower blank area.